(368ac) Process Integration Assessments of Renewably-Powered Direct Air Capture, CO2 Regeneration, and Carbon Conversion Technologies

Research Interests: CO₂ Electrolysis, H2O Electrolysis, Carbon Conversion, Techno-Economic Assessment, Carbon Management, Carbon Dioxide Removal, Process Modeling

The capture of carbon dioxide (CO₂), either from concentrated or diluted sources using CO₂ removal (CDR) technologies, is necessary to achieve carbon neutrality targets. One of the most promising CDR pathways is hydroxide-based direct air capture (DAC), which uses air contactors to enable the reaction between hydroxides and air-sourced CO₂ to produce a mixture of (bi)carbonates. Such a chemical reaction is spontaneous and kinetically fast with an enthalpy of reaction of -191.73 kJ per mole. Although this process is promising for CO₂ capture from diluted sources, uncertainty around the utilization of the captured CO₂ persists.

Storing the captured CO₂ in minerals or underground is needed at giga-tonne scales. However, achieving a circular carbon economy that moves us closer to carbon neutrality requires leveraging some of the captured CO₂ as a building block for fuels and chemicals. Early studies of DAC leveraged the calcium looping technology, which was adapted from the cement industry, to thermally liberate the CO₂ in a gaseous form and regenerate the liquid solvent to re-capture fresh CO₂ from air. Indeed, we assessed the integration of hydroxide-based DAC with reverse water gas shift (RWGS) and with CO₂ electrolysis (CO₂ER) to compare the techno-economic performance of DAC-RWGS with DAC-CO₂ER for cleaner syngas production. For both processes, we provide low-carbon hydrogen from water electrolysis to synthesize the syngas molecules. We found that syngas cost ranges from $0.70 to $1.85 per t-syngas–equivalent to 3.50-9.25 times the market syngas price. The high product cost is mostly caused by the high electricity cost in both pathways from electrolysis processes, which contributes 45-46% of the total product cost. Therefore, finding alternative integration pathways that achieve the goal of designing an efficient capture-and-conversion system is still needed.

One of the promising routes is the integration of air contactors with (bi)carbonate electrolysis, presenting an elegant solution that achieves the in-situ regeneration of gaseous CO₂ and the production of more valuable products, such as CO or syngas (i.e., a mixture of CO and H₂). However, the ability of the (bi)carbonate electrolyzer to regenerate the capture solvent is still uncertain. In 2024, we assessed this pathway from a process systems engineering perspective and found it to be mass-balance and cost limited. We concluded that additional pH shifting steps would be required to overcome this issue. Namely, bipolar membrane electrodialysis (BPMED) stacks that convert salts into separate acidic and basic streams could be used to liberate gaseous CO₂ from (bi)carbonate solutions and re-capture fresh CO₂ from air, respectively. However, it is still unknown whether this pathway is economically feasible, especially when integrated with gaseous CO₂ electrolysis and powered by intermittent renewables. The last project of my PhD will explore this topic in more detail, elucidating not only the process-process integration opportunities and challenges, but the power-process considerations as well.

This poster covers the three projects that compose my overall PhD work. I will discuss methodologies and findings of these projects and will attempt to connect the dots at the system level, providing research-informed guidance to the pursuit of emerging technologies in this space.